1. Field of the Invention
The present invention relates to method and apparatus for perforating fibrous board surfaces in non-repetitive patterns. The board is especially suited for use as acoustical tiles and panels.
2. Description of the Prior Art
Known methods and apparatus for perforating fibrous board surfaces employ pattern forming members which are capable of forming only the single pattern associated with the particular member. Proudfoot et al U.S. Pat. No. 2,791,289 discloses the formation of holes and fissures in board surfaces by eroding selected portions of the board surface through a stencil member by sand-blasting. Another known method is to use cutting or pressing dies, roll or punch type, to press or cut perforations into the board surface, as taught in Carlson et al U.S. Pat. No. 3,202,025 and Norsted U.S. Pat. No. 3,230,813. However, complete randomness is not possible using a finite number of stencils or dies and repetitive patterns result. In Thomas et al U.S. Pat. No. 3,077,945, varients of a generalized pattern are formed on board surfaces by varying the contours of already formed standard fissures. However, the number of varients is limited by the number of varient forms, and repetitive patterns result. All of the foregoing processes require the use of multiple dies, stencils, etc. to vary the pattern, which entails great expense and complexity, and none are capable of producing a random, non-repetitive pattern.
The present invention obviates the foregoing disadvantages and drawbacks and is capable of producing a random, non-repetitive pattern in a fibrous board product.